1. Field of the Invention
The invention relates to the field of televisions capable of displaying side by side pictures of substantially equal size and comparable picture quality from different sources, and in particular, to such televisions having a wide display format ratio screen. Most televisions today have a format display ratio, horizontal width to vertical height, of 4:3. A wide format display ratio corresponds more closely to the display format ratio of movies, for example 16:9. The invention is applicable to both direct view televisions and projection televisions.
2. Description of Related Art
Televisions having a format display ratio of 4:3, often referred to as 4.times.3, are limited in the ways that single and multiple video signal sources can be displayed. Television signal transmissions of commercial broadcasters, except for experimental material, are broadcast with a 4.times.3 format display ratio. Many viewers find the 4.times.3 display format less pleasing than the wider format display ratio associated with the movies. Televisions with a wide format display ratio provide not only a more pleasing display, but are capable of displaying wide display format signal sources in a corresponding wide display format. Movies "look" like movies, not cropped or distorted versions thereof. The video source need not be cropped, either when converted from film to video, for example with a telecine device, or by processors in the television.
Televisions with a wide display format ratio are also suited to a wide variety of displays for both conventional and wide display format signals, as well as combinations thereof in multiple picture displays. However, the use of a wide display ratio screen entails numerous problems. Changing the display format ratios of multiple signal sources, developing consistent timing signals from asynchronous but simultaneously displayed sources, switching between multiple sources to generate multiple picture displays, and providing high resolution pictures from compressed data signals are general categories of such problems. A wide screen television according to various inventive arrangements is capable of providing high resolution, single and multiple picture displays, from single and multiple sources having similar or different format ratios, and with selectable display format ratios. This invention is directed in particular to providing high resolution pictures from compressed data signals.
Television apparatus with conventional format display ratios can be equipped for displaying multiple pictures, for example from two video sources. The video sources may be the tuner in the television, a tuner in a video cassette recorder, a video camera, and others. In a mode often referred to as picture-in-picture (PIP), the tuner in the television provides a picture filling most of the screen, or display area, and an auxiliary video source provides a small inset picture generally within the boundaries of the larger picture. A PIP display mode in a wide screen television apparatus is shown in FIG. 1(c). In many instances, the inset picture can be positioned in a number of different locations. Another display mode is often referred to as channel scan, wherein a large number of small pictures, each from a different channel source, fill the screen in a freeze frame montage. There is no main picture, at least in terms of size. A channel scan display mode in a wide screen television apparatus is shown in FIG. 1(i). In wide screen television apparatus, other display modes are possible. One is referred to as picture-outside-picture (POP). In this mode, several inset auxiliary pictures can share a common boundary with a main picture. A POP display mode in a wide screen television apparatus is shown in FIG. 1(f). another mode particularly suited for a wide screen television is side by side pictures of substantially the same size, from different video sources, for example two different channels. This mode is illustrated for a wide screen television in FIG. 1(d) for two 4:3 video sources. It will be appreciated that this mode can be considered a special case of the POP mode.
The synchronization of asynchronous video signals often requires that successive fields of one of the signals be stored in one or more field memories. Limitations on memory space can impose a need to compress the data of the stored signal to enable storage in limited capacity field memories, or a need to sample the data at a lower sampling rate than the other video signal. This can result in lower quantization resolution for the stored video signal when the pictures are displayed, particularly if the stored picture is larger than a typically small PIP or POP. In the side by side picture mode described above, where the main and auxiliary video signals are displayed side by side, and with equal size, a lower quantization resolution in the auxiliary picture can be apparent from even a casual comparison of the two pictures. It would be desirable for pictures from different video sources to be displayed side by side, for example on a wide screen television, with substantially comparable picture quality, even when one of the signals has a lower quantization resolution.